Transparent substrate which can be used alternatively or cumulatively for thermal control, electromagnetic armour and heated glazing

ABSTRACT

The subject of the invention is a transparent substrate, especially made of glass, provided with a thin-film stack comprising a plurality of functional layers, characterized in that said thin-film stack comprises at least three silver-based functional layers, in that said stack has a resistance R □ &lt;1.5Ω per square and in that said substrate may undergo at least one transformation operation involving a heat treatment at a temperature of at least 500° C., so as to make it possible to achieve, using the substrate, alternatively or cumulatively, thermal control and/or electromagnetic shielding and/or heating.

The present invention relates to the field of glazing that can be usedalternatively or cumulatively in three particular applications, namelythermal control (solar control and thermal insulation), electromagneticshielding and heated windows, while still preferably being able toundergo at least one transformation operation involving a heat treatmentat a temperature of at least 500° C. (this may be in particular atoughening, annealing or bending operation).

Thermal control is the possibility of acting on solar radiation and/orlong-wavelength infrared radiation passing through glazing thatseparates an outdoor environment from an indoor environment, either foroutward reflection of the solar radiation (“solar control” glazing) orfor inward reflection of the infrared radiation of wavelength greaterthan 5 μm (thermal insulation with glazing called in particular“low-emissivity glazing”).

Electromagnetic shielding is the possibility of eliminating, or at thevery least reducing, the propagation of electromagnetic waves throughglazing. This possibility is often combined with the possibility ofacting on the infrared radiation passing through the glazing. Thisapplication is advantageous in the electronics field, especially for theproduction of electromagnetically shielded windows, also called“electromagnetic filters”, which are intended for example to be placedon the faceplate of a display screen using plasma technology.

A heated window is a window whose temperature may rise when it issubjected to an electrical current. This type of window has applicationsin automobiles, or even in buildings, for the production of glass panesthat prevent the formation, or that eliminate, ice or misting, or elsethat suppress the sensation of a cold wall near the glazing.

The present invention relates more particularly to a transparentsubstrate, especially made of glass, which is provided with a thin-filmstack comprising a plurality of functional layers, said substrate beingable to be used, alternatively, or cumulatively, for thermal control,electromagnetic shielding and heated windows.

It is known to produce thin-film stacks to achieve thermal control, moreprecisely solar control, which are capable of simultaneously preservingtheir thermal properties and their optical properties after heattreatment, while minimizing any appearance of optical defects, thechallenge then being to therefore have thin-film stacks of constantoptical/thermal performance, whether or not they subsequently undergoone or more heat treatments.

A first solution was proposed in European patent application No EP 718250. This recommended the use, above the silver-based functionallayer(s), of oxygen-diffusion barrier layers, especially those based onsilicon nitride, and the direct deposition of silver layers on thesubjacent dielectric coating, without interposition of priming layers ormetal protection layers. That patent application describes in particulara stack of the type:

substrate/Si₃N₄ or AlN/ZnO/Ag/Nb/ZnO/Si₃N₄.

A second solution was proposed in European patent application No EP 847965. This relies on stacks comprising two silver layers and describesthe use both of a barrier layer on top of the silver layers (aspreviously) and of an absorbent or stabilizing layer which is adjacentto said silver layers and allows them to be stabilized.

That patent application describes in particular a stack of the type:

substrate/SnO₂/ZnO/Ag1/Nb/Si₃N₄/ZnO/Ag2/Nb/SnO₂/Si₃N₄.

In the above two solutions, it should be noted that the presence of theabsorbent “overblocker” metal layer, made of niobium in this case, oreven titanium, on the silver layers makes it possible to prevent thesilver layers from coming into contact with an oxidizing or nitridingreactive atmosphere during deposition by reactive sputtering of the SnO₂layer or the Si₃N₄ layer respectively.

A third solution has since been disclosed in International patentapplication No WO 03/01105. This proposes to deposit the absorbent“blocker” metal layer not on the (or each) functional layer, butunderneath, so as to allow the functional layer to be stabilized duringthe heat treatment and to improve the optical quality of the stack afterheat treatment.

That patent application describes in particular a stack of the type:

substrate/Si₃N₄/ZnO/Ti/Ag1/ZnO/Si₃N₄/ZnO/Ti/Ag2/ZnO/Si₃N₄.

However, within the thickness ranges disclosed, such a stack cannot beused to produce a heated window or electromagnetically shielded windowof acceptable appearance (optical characteristics).

The prior art also teaches thin-film stacks on a substrate that can beused for thermal control and for heated windows when they are subjectedto an electrical current. International patent application No WO01/14136 thus discloses a stack consisting of a silver double layer thatwithstands a toughening heat treatment, which can be used for solarcontrol and for producing heat when it is subjected to an electricalcurrent. However, the resistivity of this stack does not allow trueeffective electromagnetic shielding to be achieved as its resistance persquare R_(□) cannot be close to, and a fortiori less than, 1.5 ohms persquare.

In addition, for heated window application in automobiles, this highresistance per square requires the use of a battery with a high voltageacross its terminals (around 42 volts, the standard voltage available onthe market) in order to be able to heat over the entire height of thewindow. Specifically, by applying the formula P(W)=U²/(R_(□)×h²), ifR_(□)=1.5 ohms per square, to achieve P=600 W/m² (the estimated powerdissipated for correct heating) and to obtain a heating height h>0.8meters, it is necessary that U>24 volts.

It is also known to produce thin-film stacks for electromagneticshielding using a substrate provided with an electromagnetic protectionstack providing good electromagnetic protection and allowing the user toeasily see the image display thanks to a high light transmittancetogether with a low reflectance.

To achieve electromagnetic shielding, the prior art also teaches, fromInternational patent application No WO 01/81262, a stack in particularof the type:

substrate/Si₃N₄/ZnO/Ag1/Ti/Si₃N₄/ZnO/Ag2/Ti/ZnO/Si₃N₄.

This stack can withstand a toughening or bending heat treatment.However, this stack does not make it possible to achieve a resistanceper square that is much less than 1.8 ohms per square with opticalcharacteristics (T_(L), R_(L), color, etc.) that are deemed to beacceptable, and especially a low light reflection R_(L) in the visible.

Silver-film-based stacks are manufactured in very complex manufacturingunits.

The major drawback of the prior art lies in the fact that it isessential to make major modifications to the production line when it isdesired to use the production line to manufacture, on the substrate, athin-film stack that does not have the same application(s) as the stackmanufactured previously on this same line.

In general, this operation lasts from several hours to several days, itis tedious and entails a very substantial loss of money, as it is notpossible to produce glazing during this transition/adjustment period.

In particular, whenever the material of the target differs from oneproduct to the next, the chamber must be returned to atmosphericpressure before the target is changed, then the chamber must be pumpeddown to a vacuum (of the order of 10⁻⁶ bar), which is obviously timeconsuming and tedious.

The object of the invention is therefore to alleviate these drawbacks byproposing a substrate with a thin-film stack and a manufacturing processof this substrate that make it possible to obtain a product that can beused, alternatively or cumulatively, for thermal control and/orelectromagnetic shielding and/or heating.

In particular, the object of the invention is to make it possible toproduce a large range of products without having to open the depositioninstallation in order to change target, so as to save time needed forventing to the atmosphere and above all the time to recreate a vacuum inthe installation after the target has been changed.

The present invention thus proposes a particular stack, defined in termsof the composition of the various layers and their thickness, which canbe used for all these applications at the same time, but also a type ofstack, defined in terms of composition of the various layers, ofthickness ranges and/or of optical characteristics, in which certainthickness values favor use for a given application. This stack isnoteworthy in that it has a low resistance per square (R_(□)<1.5, oreven ≦1.3Ω per square) while still substantially maintaining itscharacteristics when it is subjected to a heat treatment of the bendingor toughening type.

Thus, by virtue of this type of stack according to the invention, tomanufacture stacks intended for a single specific application or onlytwo specific applications or the three specific applications, one ormore parameters can be changed, such as the thickness of certain layers,but the composition generally remains identical. A few hours thussuffice for modifying the production line and switching from themanufacture of a product having one or more preferred applications toanother product having one or more other preferred applications.

Thus, one subject of the present invention is a transparent substrate,especially made of glass, as claimed in claim 1. This substrate isprovided with a thin-film stack comprising a plurality of functionallayers, said thin-film stack comprising at least three silver-basedfunctional layers, the said stack having a resistance R_(□)<1.5, or even≦1.3Ω per square, and said substrate being able to undergo at least onetransformation operation involving a heat treatment at a temperature ofat least 500° C., so as to be able to produce, using the substrate,alternatively or cumulatively, thermal control and/or electromagneticshielding and/or heating.

The expression “said substrate may undergo at least one transformationoperation involving a heat treatment at a temperature of at least 500°C.” is understood to mean the fact that the treatment does not degradethe optical quality nor does it cause the appearance of pitting visibleto the naked eye and/or of haze in transmission, when carrying out abending, toughening or annealing operation at a temperature of at least500° C. or upper than 500° C.

Moreover, the resistance RD claimed is, unless otherwise indicated,measured before this optional heat treatment.

In a first application, for the production of automobile windows, thesubstrate according to the invention has a light transmission T_(L)≧70%and a resistance R_(□)<1.5, or even ≦1.3, or better still ≦1.2Ω persquare.

In a second application, for the production of building windows, thetransparent substrate according to the invention has a lighttransmission T_(L)≧40%, or even ≧50%, preferably with a light reflectionin the visible R_(L)≦10%, or even ≦8% and when it is combined with atleast one other substrate to form a glazing assembly, this glazingassembly has a selectivity ≧2, or even >2.

It will be recalled here that selectivity is defined by the ratio of thelight transmission (T_(L)) to the solar factor (SF), i.e. T_(L)/SF, thesolar factor representing the sum of the direct energy transmission(T_(E)) of the glazing and of the energy absorbed by the glazing andretransmitted into the interior of the building.

In a third application, for producing electromagnetically shieldedglazing, the transparent substrate according to the invention has alight transmission T_(L)≧40%, or even ≧50%, and even better still ≧55%,and a resistance R_(□)≦1.2, or even ≦1Ω per square.

The major advantage resulting from the fact that the electromagneticallyshielded substrate withstands a heat treatment of the toughening type orthe like is that it is thus possible to use a lighter substrate.Furthermore, experiments have shown that it is always more practical,from the industrial standpoint, to use a substrate coated with a stackthat withstands a heat treatment rather than to use a substrate that hasundergone a heat treatment and then a stack deposited on top of it.

The substrate on which the stack is deposited is preferably made ofglass.

Usually, within the context of the present invention, since the stack isdeposited on the substrate, this substrate establishes a zero level andthe layers deposited on top establish superjacent levels that may benumbered in an increasing order by whole numbers in order to distinguishthem. In the present document, the numbering is used only to distinguishthe functional layers and their order of deposition.

The term “upper layer” or “lower layer” is understood to mean a layerthat is not necessarily deposited strictly on top of or beneath,respectively, the functional layer during production of the stack, itbeing possible for one or more layers to be inserted therebetween. Sinceeach functional layer is associated with one or more layers depositedbeneath or on top of the functional layer whose presence in the stack isjustified with respect to this functional layer, it may be said that theassociation, i.e. functional layer with its one or more subjacent and/orsuperjacent layer(s), produces a “feature”.

According to a variant of the invention, the substrate comprises atleast four silver-based functional layers.

The total thickness of the silver-based functional layers is preferablygreater than or equal to 25 nm. This total thickness is preferablysubstantially between 35 and 50 nm when the stack comprises threefunctional layers and substantially between 28 and 64 nm when the stackcomprises at least four functional layers. In a variant, the sum of thethicknesses of the silver layers is less than 54 nm.

In a variant of the invention, the substrate comprises at least threeidentical features of functional layers, each functional layer beingassociated in each functional feature with at least one subjacent and/orsuperjacent layer.

According to another variant of the invention, at least one functionallayer, and preferably each functional layer, is located between at leastone lower dielectric layer and one upper dielectric layer, saiddielectric layers preferably being based on ZnO, optionally doped withaluminum.

According to a variant of the invention, at least one functional layer,and preferably each functional layer, comprises an upper layer based onSi₃N₄, AlN or based on a mixture of the two.

According to a variant of the invention, the substrate is directlycoated with a layer based on Si₃N₄ AlN or based on a mixture of the two.

In a variant of the invention, in at least one functional feature, andpreferably in each functional feature, an upper absorbent metal layer(called an “overblocker”), preferably based on Ti, is located betweenthe silver-based functional layer and at least one upper dielectriclayer.

According to another variant of the invention, in at least onefunctional feature, and preferably in each functional feature, a lowerabsorbent metal layer (called an “underblocker”), preferably based onTi, is located between at least one lower dielectric layer and thesilver-based functional layer.

The upper or lower absorbent metal layer may also consist of a metal orof an alloy based on nickel, chromium, niobium, zirconium, tantalum oraluminum.

According to a variant of the invention, at least one functionalfeature, and preferably each functional feature, has the followingstructure: ZnO/Ag/ . . . ZnO/Si₃N₄ and preferably the followingstructure: ZnO/Ag/Ti/ZnO/Si₃N₄.

According to this variant, the thicknesses of the constituent layers ofsaid feature in the case of the three-layer stack are preferably:

ZnO/Ag/ . . . ZnO/Si₃N₄ and preferably ZnO/Ag/Ti/ZnO/Si₃N₄

5 to 15/10 to 17/ . . . 5 to 15/25 to 65 nm and preferably 5 to 15/10 to17/0.2 to 3/5 to 15/25 to 65 nm, or 7 to 15/10 to 17/ . . . 7 to 15/25to 65 nm and preferably 7 to 15/10 to 17/0.2 to 2/7 to 15/25 to 65 nm.

Also according to this variant, the thicknesses of the constituentlayers of said feature in the case of the four-layer stack arepreferably:

ZnO/Ag/ . . . ZnO/Si₃N₄ and preferably ZnO/Ag/Ti/ZnO/Si₃N₄

5 to 15/7 to 15/ . . . 5 to 15/23 to 65 nm and preferably 5 to 15/7 to15/0.2 to 3/5 to 15/23 to 65 nm, or 7 to 15/7 to 15/ . . . 7 to 15/23 to65 nm and preferably 7 to 15/7 to 15/0.2 to 2/7 to 15/23 to 65 nm.

The subject of the invention is also a process for manufacturing atransparent substrate, especially made of glass, provided with athin-film stack comprising a plurality of functional layers,characterized in that at least three silver-based functional layers aredeposited on said substrate, in that said stack has a resistanceR_(□)<1.5, or even ≦1.3Ω per square and in that said substrate mayundergo at least one transformation operation involving a heat treatmentat a temperature of at least 500° C., so as to make it possible toproduce, alternatively or cumulatively by means of the substrate,thermal control and/or electromagnetic shielding and/or heating.

According to a variant of the invention, at least four silver-basedfunctional layers are deposited on said substrate.

The total thickness of the silver-based functional layers deposited ispreferably greater than or equal to 25 nm. This total thickness ispreferably substantially between 35 and 50 nm when the stack comprisesthree functional layers and substantially between 28 and 64 nm when thestack comprises at least four functional layers.

According to a variant of the invention, at least three identicalfeatures of functional layers are deposited on said substrate, eachfunctional layer being associated in each functional feature with atleast one subjacent and/or superjacent layer.

According to a variant of the invention, for at least one functionallayer, and preferably for each functional layer, at least one lowerdielectric layer is deposited beneath said functional layer and an upperdielectric layer is deposited on said functional layer, said dielectriclayers being preferably based on ZnO, optionally doped with aluminum.

According to a variant of the invention, an upper layer based on Si₃N₄,AlN or based on a mixture of the two is, deposited on top of at leastone functional layer, and preferably on top of each functional layer.

According to a variant of the invention, said substrate is directlycoated with a layer based on Si₃N₄, AlN or based on a mixture of thetwo, previously deposited when all the other layers were deposited.

According to a variant of the invention, in at least one functionalfeature, and preferably in each functional feature, an upper absorbentmetal layer, preferably based on Ti, is deposited on top of thesilver-based functional layer and beneath at least one upper dielectriclayer.

According to another variant of the invention, in at least onefunctional feature, and preferably in each functional feature, a lowerabsorbent metal layer, preferably based on Ti, is deposited on top of atleast one lower dielectric layer and beneath the silver-based functionallayer.

According to a variant of the invention, at least one functional featuredeposited, and preferably each functional feature deposited, has thefollowing structure: ZnO/Ag/ . . . ZnO/Si₃N₄ and preferably thefollowing structure: ZnO/Ag/Ti/ZnO/Si₃N₄.

According to this variant of the invention, the thicknesses of theconstituent layers deposited of said feature in the case of thethree-layer stack are preferably:

ZnO/Ag/ . . . ZnO/Si₃N₄ and preferably ZnO/Ag/Ti/ZnO/Si₃N₄

5 to 15/10 to 17/ . . . 5 to 15/25 to 65 nm and preferably 5 to 15/10 to17/0.2 to 3/5 to 15/25 to 65 nm, or 7 to 15/10 to 17/ . . . 7 to 15/25to 65 nm and preferably 7 to 15/10 to 17/0.2 to 2/7 to 15/25 to 65 nm.

Also according to this variant of the invention, the thicknesses of theconstituent layers deposited of said feature in the case of thefour-layer stack are preferably:

ZnO/Ag/ . . . ZnO/Si₃N₄ and preferably ZnO/Ag/Ti/ZnO/Si₃N₄

5 to 15/7 to 15/ . . . 5 to 15/23 to 65 nm and preferably 5 to 15/7 to15/0.2 to 3/5 to 15/23 to 65 nm, or 7 to 15/7 to 15/ . . . 7 to 15/23 to65 nm and preferably 7 to 15/7 to 15/0.2 to 2/7 to 15/23 to 65 nm.

According to a variant of the invention, the functional features aredeposited by passing said substrate several times through a singlemanufacturing device.

According to this variant of the invention, when said stack comprisesfour silver-based functional layers, the features are deposited inpairs, by passing said substrate twice through a single manufacturingdevice under depositing conditions that are substantially identical forthe two passes and preferably in keeping the substrate in vacuum betweenthe two passes.

Also according to this variant of the invention, the thicknesses of thedeposited layers are preferably substantially identical during each ofthe two passes.

Moreover, when the substrate according to the invention undergoes atransformation operation involving a heat treatment at a temperature ofat least 500° C., its resistance R₅ is preferably reduced by at least10%, or even at least 15%.

The subject of the invention is also glazing for thermal control and/orelectromagnetic shielding and/or heating, which incorporates at leastone substrate according to the invention.

The subject of the invention is also the use of the substrate accordingto the invention for producing, alternatively or cumulatively, thermalcontrol and/or electromagnetic shielding and/or heating.

Advantageously, the savings made by implementing the process accordingto the invention when producing a stack according to the invention areenormous, since it is no longer necessary to stop the production linefor several days or at least several hours when it is desired to producestacks for one or more different application(s). A few hours suffice formodifying the production parameters on the line and to obtain a saleableproduct for the desired application(s).

Also advantageously, the substrate according to the invention can beused for producing monolithic glazing, double or triple glazing orlaminated glazing and to achieve, alternatively or cumulatively, thermalcontrol and/or electromagnetic shielding and/or heating.

Thus, for the automobile application, it is possible to producelaminated glazing that incorporates a substrate according to theinvention, this glazing achieving, at the same time:

-   -   thermal control (more precisely solar control for reflecting        solar radiation on the outside of the vehicle);    -   electromagnetic shielding for protecting the interior of the        vehicle from external electromagnetic radiation; and    -   heating, for melting ice or for evaporating condensation.

Likewise, for the building application, it is possible to produce doubleglazing that incorporates a substrate according to the invention, thisglazing achieving, at the same time:

-   -   thermal control (solar control for reflecting solar radiation on        the outside of the room equipped with the glazing and/or thermal        insulation for reflecting internal radiation into the room        equipped with the glazing);    -   electromagnetic shielding, for protecting the interior of the        room equipped with the glazing from external electromagnetic        radiation; and    -   heating, for eliminating condensation or preventing its        formation, and for preventing the sensation of a “cold wall”        near the glazing.

Advantageously, such glazing incorporating a substrate according to theinvention has attractive colors in transmission and in reflection.

The present invention will be more clearly understood on reading thedetailed description below of non-limiting illustrative examples and onexamining the figures appended hereto:

FIG. 1 illustrates the values of the light reflection to the outside ofExamples 11 and 13 as a function of the wavelength λ;

FIG. 2 illustrates the light transmission values, of Example 21according to the invention and Comparative Example 22 respectively, as afunction of the wavelength λ, and also the Parry-Moon curve for thesolar energy density D as a function of the wavelength λ;

FIG. 3 illustrates the light transmission values, of Example 21according to the invention and Comparative Example 22 respectively, as afunction of the wavelength λ and also the sensitivity to the human eye,Y, on a normalized scale H;

FIG. 4 illustrates the light transmission values, of Examples 23 and 24according to the invention and Comparative Example 25 respectively, as afunction of the wavelength λ, and also the Parry-Moon curve for thesolar energy density D as a function of the wavelength λ; and

FIG. 5 illustrates a diagram of an electromagnetically shielded glazingassembly employing the substrate according to the invention.

1—Examples of Stacks for Heated Windows and More Particularly forWindshields Supplied with 12 V

The dissipated power for correct heating is generally estimated to be600 W/m².

Specifically, P(W)=U²/(R_(□)×h²). If U=12 V, then it is necessary thatR_(□)=1 ohm per square for h=50 cm; h corresponding to the height of the“window” in which the heating is carried out, so as to prevent theformation of condensation and/or ice (in practice, the voltage U is from12 to 14 V, which corresponds to the voltage across the terminals of thebatteries of most motor vehicles currently produced; however, thisvoltage could be between 12 and 24 V.

For the automobile application, a stack having the followingcharacteristics (as laminated glazing) may be deemed to be satisfactory:

-   -   R_(□)≦1.2 ohms per square;    -   good quality (no defects perceptible to the naked eye) after        bending;    -   T_(L)≧70% and limited R_(L);    -   color in reflection deemed to be attractive (preferably a*≦0 and        b*≦0);    -   satisfactory mechanical and chemical durability.

Solutions having two silver layers encapsulated in dielectrics do notmake it possible to obtain both a T_(L)≧70% and a resistance R_(□)≦1.2Ωper square and an acceptable color.

To achieve the desired result, it appears preferable:

-   -   to position the thin-film stack comprising the functional layers        on face 3 (face 1 being the face furthest to the outside of the        vehicle and face 4 being the innermost face); and    -   to deposit more than two silver layers, taking into account the        necessary total thickness of the silver layers.

Examples of the construction of stacks according to the invention aregiven below with stacks comprising three functional layers (Examples 11,12 and 14) and with four functional layers (Examples 15 and 16), theresults having been measured after a toughening operation at 620° C. forabout 8 minutes.

Example 11 According to the Invention Three-Layer: Layer Si₃N₄ ZnO Ag1ZnO Si₃N₄ ZnO Ag2 ZnO Si₃N₄ ZnO Ag3 ZnO Si₃N₄ Thickness 37 7 12.5 8 49 712.5 8 53 7 12.5 8 29 (nm)outside/glass (2.1 mm)/PVB (0.76 mm)/Ag3/Ag2/Ag1/glass (1.6 mm)/inside

Example 12 According to the Invention, Three-Layer:

Same stack as in Example 11 but also with a titanium overblocker on topof each functional layer (thickness around 0.5 nm to 1 nm).

Example 13, Two-Layer Comparative Example: Layer Si₃N₄ ZnO Ag1 ZnO Si₃N₄ZnO Ag2 ZnO Si₃N₄ Thickness 24 8 8 6 70 8 7 6 26 (nm)outside/glass (2.1 mm)/PVB (0.76 mm)/Ag3/Ag2/Ag1/glass (1.6 mm)/insidewith, in addition, a titanium underblocker beneath each functional layer(thickness around 0.5 nm to 1 nm)

Example 14 According to the Invention, Three-Layer: Layer Si₃N₄ ZnO Ag1ZnO Si₃N₄ ZnO Ag2 ZnO Si₃N₄ ZnO Ag3 ZnO Si₃N₄ Thickness 37 7 12.5 8 52 713.5 8 52 7 14 8 31 (nm)outside/glass (2.1 mm)/PVB (0.76 mm)/Ag3/Ag2/Ag1/glass (1.6 mm)/inside

Measured Technical Characteristics of the Laminated Glazing: R_(□) T_(L)T_(E) Ext. R_(L) R_(E) Example (Ω/□) (%) (%) (%) a*(R_(ext)) b*(R_(ext))(%) 11 1.09 70.4 30.4 12.1 −10.9 11.7 46.0 12 1.00 70.1 30.8 14.2 −9.37.9 46.1 13 4.60 76.1 46.1 17.8 −4.8 −1.9 29.8 14 1.00 70.5 31.4 11.5−7.5 2.7 44.8

Example 15 According to the Invention, Four-Layer: Si₃N₄ ZnO Ag1 ZnOSi₃N₄ ZnO Ag2 ZnO Si₃N₄ ZnO Ag3 ZnO Si₃N₄ ZnO Ag4 ZnO Si₃N4 30 8 7 7 578 7 8 58 8 7.5 7 50 8 7.5 7 23outside/glass (2.1 mm)/PVB (0.76 mm)/Ag3/Ag2/Ag1/glass (1.6 mm)/inside

Example 16 According to the Invention, Four-Layer: Si₃N₄ ZnO Ag1 ZnOSi₃N₄ ZnO Ag2 ZnO Si₃N₄ ZnO Ag3 ZnO Si₃N₄ ZnO Ag4 ZnO Si₃N₄ 28 8 9 7 588 9 7 56 8 9 7 58 8 9 7 28outside/glass (2.1 mm)/PVB (0.76 mm)/Ag3/Ag2/Ag1/glass (1.6 mm)/inside

This Example 16 is obtained by passing the substrate twice through aunit for stack having two silver layers.

Measured Technical Characteristics of the Laminated Glazing: R_(□) T_(L)T_(E) Ext. R_(L) R_(E) Example (Ω/□) (%) (%) (%) a*(R_(ext)) b*(R_(ext))(%) 15 1.4 70.1 38.9 11.3 6.1 −9.9 31.8 16 1.03 70.3 31.7 8.3 −1.8 −2.540.4

The resistivity of the stacks, calculated from the resistance per squareobtained by contactless measurement using a Nagy device, is around4.2×10⁻⁶ ohms.cm for the three-layer examples according to theinvention, Examples 11 and 12, whereas it is around 7×10⁻⁶ ohms.cm forthe two-layer Comparative Example 13.

In the Examples 11, 12, 14, 15 and 16 according to the invention, theT_(L), R_(L) and color values are relatively stable.

The energy reflection values are very high, which was expected owing tothe cumulative thickness of silver (3×12.75 nm). Excellent selectivity(T_(L)/FS close to or even greater than 2 in the case of a laminatedspecimen) was obtained.

The resistivity of the silver layers included in the three-layer stackscomprising silver layers having a thickness of about 13 nm issurprisingly low compared with the values obtained with a two-layerstack comprising silver layers having a thickness of about 8 to 9 nm.

The optical quality of the four examples according to the inventionafter bending is satisfactory—there is no haze or corrosion pittingobservable under normal conditions.

The chemical and mechanical durability of these stacks according to theinvention is also very good.

2—Examples of Stacks for Thermal-Control, Particularly Solar-Control,Glazing for Buildings

The performance of a solar-controlled product is evaluated on the basisof the “selectivity” criterion, that is to say the ratio of the lighttransmission (T_(L)) of the glazing to the percentage amount of solarenergy penetrating the inside of the building (solar factor or SF). Inorder to obtain the highest possible selectivity, while stillmaintaining a good level of light transmission (needed for the comfortof the occupants of the rooms), it is important to find glazing thatwill ensure as abrupt as possible a transmission cutoff between thevisible range and the infrared range, and thus prevent the energycontained in this part of the spectrum being transmitted (Parry-Moon(PM) curve). The ideal spectrum for solar-controlled glazing istherefore a step function, ensuring transmission in the visible butcompletely cutting off the infrared.

The definition of stacks having three silver layers and four silverlayers according to the invention makes it possible to increase thisselectivity. This is because, for well-chosen silver thicknesses anddielectric thicknesses, the transmission spectrum of glazing comprisingthis type of stack approaches a step function and therefore makes itpossible, for the same level of transmission, for the selectivity to besubstantially increased. This can be achieved without losing the colorneutrality of the glazing, both in transmission and in reflection.

Examples of stack constructions are given below with stacks comprisingthree functional layers (Examples 21 and 23) and with four functionallayers (Example 24), these being compared with stacks having twofunctional layers (Examples 22 and 25), for obtaining, respectively, atransmission level of 50% (Examples 21 and 22) and a transmission levelof 60% (Examples 23 to 25) and optimized selectivity.

All these examples were produced according to the following scheme:

outside/glass (6 mm)/stack/space(15 mm)/glass (6 mm)/inside,

with a space filled with a mixture of 90% argon and 10% dry air, and theresults given below were measured after a toughening operation at 620°C. for about 8 minutes.

Three-Layer Example 21 According to the Invention and ComparativeTwo-Layer Example 22 each having a 50% Light Transmission (LayerThicknesses in nm): Ex Glass Si₃N₄ ZnO Ag1 ZnO Si₃N₄ ZnO Ag2 ZnO Si₃N₄ZnO Ag3 ZnO Si₃N₄ 21 6 mm 35 10 16.2 10 55 10 16.2 10 55 10 16.2 10 3322 6 mm 26 10 9.2 10 63 10 19 10 20Ti overblocker layer about 1 nm in thickness was also positioned justabove each functional layer.

Measured Technical Characteristics: T_(E) T_(L) λ_(d) p_(e) R_(int)R_(ext) (PM, (%) (nm) (%) (%) L_(int)* a_(int)* b_(int)* (%) L_(ext)*a_(ext)* b_(ext)* mass 2) T_(L)/T_(E) Ex. 21 50.2 501 6.6 12.7 42.3 −3.4−3.1 13.8 43.9 −1.0 −1.3 20.0 2.51 Ex. 22 49.3 514 3.3 23.0 55.1 0.7 5.919.2 50.9 −3.1 −9.2 24.2 2.04The dominant color expressed by λ_(d) and the purity expressed by p_(e)are measured here in transmission.

Three-Layer Example 23 According to the Invention, Four-Layer Example 24According to the Invention and Comparative Two-Layer Example 25, EachHaving a 60% Light Transmission (Layer Thicknesses in nm): Ex Si₃N₄ ZnOAg1 ZnO Si₃N₄ ZnO Ag2 ZnO Si₃N₄ ZnO Ag3 ZnO Si₃N₄ ZnO Ag4 ZnO Si₃N₄ 2330 15 14 15 50 15 14 15 50 15 14 15 30 24 24 15 12.5 15 52 15 12.5 15 5215 12.5 15 52 15 12.5 15 24 25 25 10 9.5 15 52 15 17 15 17A Ti overblocker layer about 1 nm in thickness was also positioned justover each functional layer.

Measured Technical Characteristics: T_(E) T_(L) λ_(d) p_(e) R_(int)R_(ext) (PM, (%) (nm) (%) (%) L_(int)* a_(int)* b_(int)* (%) L_(ext)*a_(ext)* b_(ext)* mass 2) T_(L)/T_(E) 23 57.0 541 3.5 12.3 41.7 −0.9−8.6 12.7 42.3 −2.6 −8.7 25.2 2.26 24 58.0 537 2.9 12.6 42.2 −6.6 0.712.2 41.5 −4.5 −1.7 24.8 2.34 25 60.1 515 3.2 19.0 50.7 2.1 1.3 15.746.6 −2.2 −9.8 29.5 2.04As previous, the dominant color expressed by λ_(d) and the purityexpressed by p_(e) are measured here in transmission.

Comparison between the spectra of Examples 21, 23 and 24 according tothe invention with Comparative Examples 22 and 25 over the entire solarspectrum, illustrated in FIGS. 2 to 4, clearly shows that thethree-layer stacks make it possible to approach the step function (verysudden drop in transmission at around 780 nm—end of the visible rangeand start of the infrared range). The same applies to the four-layerstacks. Moreover, this increase in selectivity is not obtained to thedetriment of the calorimetric response of the glazing, the color inexternal reflection of the glazing being neutral (in the L*a*b* system),a* and b* being negative and of low absolute value. In addition, thecolor in transmission does not have a higher purity, which allows theoccupants of rooms to appreciate the outdoor environment in their truecolors. This point can be seen in FIG. 3, which shows the superpositionof the spectra of Examples 21 and 22 and the sensitivity of the humaneye. In fact, this graph shows that the optical filter produced usingthe thin-film stack of Example 21 is broader, in terms of wavelength,than the distribution of the sensitivity of the human eye.

3—Examples of Stacks for Electromagnetically Shielded Glazing and MoreParticularly for Plasma Screens

The structure of the stack produced for verifying the benefit of theinvention in the case of electromagnetic shielding is the following:

-   -   clear glass substrate (2 mm)/thin-film stack having at least        three functional layers.

The toughening carried out prior to the measurements was introduced byannealing the substrate provided with the stack at a temperature ofabout 620° C. for 5 minutes.

Example 31 According to the Invention, Four-Layer: Si₃N₄ ZnO Ag1 ZnOSi₃N₄ ZnO Ag2 ZnO Si₃N₄ ZnO Ag3 ZnO Si₃N₄ ZnO Ag4 ZnO Si₃N₄ 22 15 12.510 48 15 12.5 10 43 15 12.5 10 48 15 12.5 10 22with furthermore a titanium overblocker above each functional layer(thickness around 0.5 nm to 1 nm).

Example 32 According to the Invention, Four-Layer: Si₃N₄ ZnO Ag1 ZnOSi₃N₄ ZnO Ag2 ZnO Si₃N₄ ZnO Ag3 ZnO Si₃N₄ ZnO Ag4 ZnO Si₃N₄ 30 15 14 1065 15 14 10 60 15 14 10 65 15 14 10 30with furthermore a titanium overblocker above each functional layer(thickness around 0.5 nm to 1 nm).

Example 33 According to the Invention Four-Layer: Si₃N₄ ZnO Ag1 ZnOSi₃N₄ ZnO Ag2 ZnO Si₃N₄ ZnO Ag3 ZnO Si₃N₄ ZnO Ag4 ZnO Si₃N₄ 17 15 10 1537 15 10 15 34 15 10 15 37 15 10 15 17with furthermore a titanium overblocker above each functional layer(thickness around 0.5 nm to 1 nm).

Technical Characteristics Measured After Annealing: R_(□) ResistivityT_(L) R_(L) λ_(d) p_(e) Example (Ω/□) (10⁻⁶ Ω · cm) (%) (%) (nm) (%) 310.9 4.5 72 6 490 9 32 0.7 3.9 70 10 450 5 33 1.2 4.8 72 7 520 5

The dominant color expressed by λ_(d) and the purity expressed by p_(e)are measured here in reflection.

It may be seen that the toughening operation lowers the resistivity ofthe silver and slightly modifies the optical properties of the stack.Specifically, in the case of Example 31, the resistance of this stackbefore annealing was R_(□)=1.1 Ω/□ (for a resistivity of 5.5×10⁻⁶ohms.cm) i.e. a reduction of about 18%; in the case of Example 32, theresistance of this stack before annealing was R_(□)=0.9 Ω/□ (for aresistivity of 5.0×10⁻⁶ ohms.cm) i.e. a reduction of about 22%; and inthe case of Example 33, the resistance of this stack before annealingwas R_(□)=1.5 Ω/□ i.e. a reduction of about 20%. However, the tougheningoperation results in no major change to the color.

The stack according to the invention may be used in an assembly having,for example, the structure illustrated in FIG. 5, so as to produce anelectromagnetic filter for a screen using plasma technology. Thisassembly comprises:

-   -   1—an optional antireflection layer;    -   2—a substrate made of clear glass, but which could also be        tinted;    -   3—a thin-film stack having at least three functional layers;    -   4—a sheet of plastic, made of PVB, which could also optionally        be made of PSA;    -   5—an optional PET film.

The thin-film stack is thus positioned on face 2 of the assembly.

The substrate receiving the stack can be toughened after the stack hasbeen deposited.

The present invention has been described in the foregoing by way ofexample. Of course, a person skilled in the art is capable of realizingvarious alternative embodiments of the invention without therebydeparting from the scope of the patent as defined by the claims.

1. A transparent substrate, especially made of glass, provided with athin-film stack comprising a plurality of functional layers,characterized in that said thin-film stack comprises at least threesilver-based functional layers, in that said stack has a resistanceR_(□)<1.5Ω per square and in that said substrate may undergo at leastone transformation operation involving a heat treatment at a temperatureof at least 500° C.
 2. The transparent substrate as claimed in claim 1,characterized in that it has a light transmission T_(L)≧70%.
 3. Thetransparent substrate as claimed in claim 1, characterized in that ithas a light transmission T_(L)≧40% and in that when it is associatedwith at least one other substrate to form a glazing assembly, thisglazing assembly has a selectivity ≧2.
 4. The transparent substrate asclaimed in claim 1, characterized in that it has a light transmissionT_(L)≧40% and a resistance R_(□)≦1.1Ω per square.
 5. The transparentsubstrate as claimed in any one of the preceding claims, characterizedin that it comprises at least four silver-based functional layers. 6.The transparent substrate as claimed in any one of the preceding claims,characterized in that the total thickness of the silver-based functionallayers is greater than or equal to 25 nm and is preferably between 35and 50 nm when the stack comprises three functional layers and between28 and 64 nm when the stack comprises at least four functional layers.7. The transparent substrate as claimed in any one of the precedingclaims, characterized in that it comprises at least three identicalfeatures of functional layers, each functional layer being associated ineach functional feature with at least one subjacent and/or superjacentlayer.
 8. The transparent substrate as claimed in any one of thepreceding claims, characterized in that at least one functional layer,and preferably each functional layer, is located between at least onelower dielectric layer and one upper dielectric layer, said dielectriclayers preferably being based on ZnO, optionally doped with aluminum. 9.The transparent substrate as claimed in any one of the preceding claims,characterized in that at least one functional layer, and preferably eachfunctional layer, comprises an upper layer based on Si₃N₄, AlN or basedon a mixture of the two.
 10. The transparent substrate as claimed in anyone of the preceding claims, characterized in that it is directly coatedwith a layer based on Si₃N₄, AlN or based on a mixture of the two. 11.The transparent substrate as claimed in any one of the preceding claims,characterized in that, in at least one functional feature, andpreferably in each functional feature, an upper absorbent metal layer,preferably based on Ti, is located between the silver-based functionallayer and at least one upper dielectric layer.
 12. The transparentsubstrate as claimed in any one of claims 1 to 10, characterized inthat, in at least one functional feature, and preferably in eachfunctional feature, a lower absorbent metal layer, preferably based onTi, is located between at least one lower dielectric layer and thesilver-based functional layer.
 13. The transparent substrate as claimedin any one of the preceding claims, characterized in that at least onefunctional feature, and preferably each functional feature, has thefollowing structure: ZnO/Ag/ . . . ZnO/Si₃N₄ and preferably thefollowing structure: ZnO/Ag/Ti/ZnO/Si₃N₄.
 14. The transparent substrateas claimed in the preceding claim, characterized in that the thicknessesof the constituent layers of said feature in the case of the three-layerstack are: ZnO/Ag/ . . . ZnO/Si₃N₄ and preferably ZnO/Ag/Ti/ZnO/Si₃N₄ 5to 15/10 to 17/ . . . 5 to 15/25 to 65 nm and preferably 5 to 15/10 to17/0.2 to 3/5 to 15/25 to 65 nm.
 15. The transparent substrate asclaimed in claim 13, characterized in that the thicknesses of theconstituent layers of said feature in the case of the four-layer stackare: ZnO/Ag/ . . . ZnO/Si₃N₄ and preferably ZnO/Ag/Ti/ZnO/Si₃N₄ 5 to15/7 to 15/ . . . 5 to 15/23 to 65 nm and preferably 5 to 15/7 to 15/0.2to 3/5 to 15/23 to 65 nm.
 16. A process for manufacturing a transparentsubstrate, especially made of glass, provided with a thin-film stackcomprising a plurality of functional layers, characterized in that atleast three silver-based functional layers are deposited on saidsubstrate, in that said stack has a resistance R_(□)<1.5Ω per square andin that said substrate may undergo at least one transformation operationinvolving a heat treatment at a temperature of at least 500° C.
 17. Theprocess as claimed in claim 16, characterized in that at least foursilver-based functional layers are deposited on said substrate.
 18. Theprocess as claimed in claim 16 or claim 17, characterized in that thetotal thickness of the silver-based functional layers deposited isgreater than or equal to 25 nm and is preferably between 35 and 50 nmwhen the stack comprises three functional layers and between 28 and 64nm when the stack comprises at least four functional layers.
 19. Theprocess as claimed in one of claims 16 to 18, characterized in that atleast three identical features of functional layers are deposited onsaid substrate, each functional layer being associated in eachfunctional feature with at least one subjacent and/or superjacent layer.20. The process as claimed in any one of claims 16 to 19, characterizedin that, for at least one functional layer, and preferably for eachfunctional layer, at least one lower dielectric layer is depositedbeneath said functional layer and an upper dielectric layer is depositedon said functional layer, said dielectric layers being preferably basedon ZnO, optionally doped with aluminum.
 21. The process as claimed inany one of claims 16 to 20, characterized in that an upper layer basedon Si₃N₄, AlN or based on a mixture of the two is deposited on top of atleast one functional layer, and preferably on top of each functionallayer.
 22. The process as claimed in any one of claims 16 to 21,characterized in that said substrate is directly coated with a layerbased on Si₃N₄ AlN or based on a mixture of the two.
 23. The process asclaimed in any one of claims 16 to 22, characterized in that, in atleast one functional feature, and preferably in each functional feature,an upper absorbent metal layer, preferably based on Ti, is deposited ontop of the silver-based functional layer and beneath at least one upperdielectric layer.
 24. The process as claimed in any one of claims 16 to22, characterized in that, in at least one functional feature, andpreferably in each functional feature, a lower absorbent metal layer,preferably based on Ti, is deposited on top of at least one lowerdielectric layer and beneath the silver-based functional layer.
 25. Theprocess as claimed in any one of claims 16 to 24, characterized in thatat least one functional feature deposited, and preferably eachfunctional feature deposited, has the following structure: ZnO/Ag/ . . .ZnO/Si₃N₄ and preferably the following structure: ZnO/Ag/Ti/ZnO/Si₃N₄.26. The process as claimed in the preceding claim, characterized in thatthe thicknesses of the constituent layers of said feature in the case ofthe three-layer stack are: ZnO/Ag/ . . . ZnO/Si₃N₄ and preferablyZnO/Ag/Ti/ZnO/Si₃N₄ 5 to 15/10 to 17/ . . . 5 to 15/25 to 65 nm andpreferably 5 to 15/10 to 17/0.2 to 3/5 to 15/25 to 65 nm.
 27. Theprocess as claimed in claim 25, characterized in that the thicknesses ofthe constituent layers of said feature in the case of the four-layerstack are: ZnO/Ag/ . . . ZnO/Si₃N₄ and preferably ZnO/Ag/Ti/ZnO/Si₃N₄ 5to 15/7 to 15/ . . . 5 to 15/23 to 65 nm and preferably 5 to 15/7 to15/0.2 to 3/5 to 15/23 to 65 nm.
 28. The process as claimed in any oneof claims 16 to 27 characterized in that the functional features aredeposited by passing said substrate several times through a singlemanufacturing device.
 29. The process as claimed in the preceding claim,characterized in that when said stack comprises four silver-basedfunctional layers, the features are deposited in pairs, by passing saidsubstrate twice through a single manufacturing device.
 30. The processas claimed in the preceding claim, characterized in that the thicknessesof the deposited layers are substantially identical during each of thetwo passes.
 31. The process as claimed in any one of claims 16 to 30,characterized in that when said substrate undergoes a transformationoperation involving a heat treatment at a temperature of at least 500°C., its resistance R_(□) is reduced by at least 10%, or even at least15%.
 32. Glazing for thermal control and/or electromagnetic shieldingand/or heating, which incorporates at least one substrate as claimed inany one of claims 1 to
 15. 33. The use of the substrate as claimed inany one of claims 1 to 15, for producing, alternatively or cumulatively,thermal control and/or electromagnetic shielding and/or heating.